1. Field of the invention
The present invention relates to a carbonaceous sintered compact, inter alia, to a sintered compact of graphite and mesocarbon microbeads for use in valve, ball joint and the like, and more particularly to an annular slide contact fluid sealing member which encloses fluid passage to seal fluid and is in contact with valve disc or inner cylinder, to be mainly used in association with annular contact sealing member which is in contact with valve casing or outer cylinder.
2. Prior art
Several annular fluid sealing mechanisms such as valve seat of valve have been widely used heretofore. For example, as shown in FIG. 1 illustrating a partially enlarged view of a spherical valve and in FIG. 2 illustrating a ball joint section, there has been provided a fluid sealing mechanism comprising an annular sliding contact member (A) of such a rigid material as carbonaceous composite material or metal to perform sealing of fluid (gas or liquid) in tight contact with valve body being a movable section, and an annular contact sealing member B) which is disposed on the rear part between valve casing or outer cylinder and the annular sliding contact member (A) in contact with both of them to perform sealing in association with valve casing.
In the valve or joint of above construction, hard rubber, fluororesin, thermosetting resin, and composite material of any of them with inorganic material have been conventionally used as the sliding contact member (A).
Some of these materials can be satisfactorily used under relatively moderate conditions, and in fact some of them are actually used as sealing materials of valves, joints or the like. However, under the recent rapid progress of technology, the service conditions have been increasingly severe, and various problems are now identified.
For example, concerning the rubber material, deterioration thereof occurs at high temperature and brittleness occur at low temperature. Concerning the fluororesin material, dimensional change takes place resulting in incomplete sealing because of large thermal expansion coefficient in extremely low temperature range wherein LNG (liquefied natural gas) or liquid nitrogen is used as fluid. Moreover, when a valve or joint is exposed to a flame of several hundreds of degrees, another problem exists in that the material decomposes resulting in loss of its sealing function. To overcome these problems, several attempts have been proposed in which ceramics or carbon material is employed. However, ceramics are disadvantageous because ceramics are inferior in machinability although superior in heat resistance, difficult in fitting with joint face of valve disc resulting in insufficient sealing performance, and moreover are not very resistant to thermal shock.
Under such circumstances, other fluid sealing materials capable of being used under conditions of high temperature, extremely low temperature or high corrosion have been further proposed recently. That is, in the combination of valve components for sealing highly corrosive fluid, heat resistant or corrosion resistant metal is used as valve casing or valve disc, while composite of such metal with carbon material being used as sealing material.
Carbon material is certainly preferable because it resists temperatures high as 3000.degree. C. and it is physically stable. The thermal expansion coefficient of carbon material is very small as compared with other materials and corrosion resistance thereof to chemical products is also satisfactory.
Conventional carbon materials, however, have several drawbacks. For example, carbon material generally has fine through pores and is therefore gas permeable. More specifically, conventional carbon materials are usually made by the steps of mixing coke, natural graphite, etc. with pitch, grinding, molding and baking it, and as a result of such steps, fine through pores are formed due to the escape of the volatile component of pitch, off gases, etc. In the production process thereof, it is usually intended to establish certain mixing and baking conditions of forming such fine through pores for the purpose of making use of such phenomenon in view of preventing the products from being broken into pieces in the baking step.
Existence of such fine through pores brings about low sealing performance as a matter of course.
To overcome the above drawbacks when using such conventional porous carbon material, several attempts have been proposed. For example, a sliding contact member formed of a composite material of carbon material and inorganic material was proposed as disclosed in Japanese Patent Publication (examined) No. 58-18554. The inorganic material used in this proposal is prepared by impregnation of at least one inorganic binder picked up among graphite oxide, boric acid and aluminum phosphate. A non ferrous metal whose melting point is 200.degree.-1100.degree. C. or composite of these material with alloy is also used as an inorganic material. In this proposed material, problems of fluid leaking through the fine pores are solved by impregnation with foreign material. Such inorganic material impregnated with foreign material or composite material closing the through pores of carbon material can prevent gas leak to a certain extent, but the following secondary problems arise:
(1) Material impregnated with metal and salt is easily corroded resulting in the decline of sealing performance and strength, with the passage of duration of service when in contact with fluids such as acid or alkaline chemical products. PA1 (2) Since there is a large difference between the metal or salt and carbon material in terms of thermal expansion coefficient and heat conductivity, partial breakdown takes place due to such differences which eventually result in a decline of strength and sealing performance. In particular, when using a composite material of this kind in a valve or joint exposed to an extremely high temperature of not lower than 500.degree. C. otherwise to an extremely low temperature of not higher than-100.degree. C., such a problem will become serious by repeated use thereof. PA1 (3) In the production of composite material prepared by above impregnation, production process is increased which, in turn, increases production cost. PA1 (a) small frictional coefficient between the members in sliding engagement with one another; PA1 (b) sufficient mechanical strength endurable to pressure applied to valve seat by valve disc and fluid; PA1 (c) sufficient impermeability; PA1 (d) sufficient resistance to chemical products; PA1 (e) small and uniform thermal expansion coefficient capable of meeting rapid temperature change; and PA1 (f) the foregoing characteristics can be kept over the wide temperature range from extremely low temperature to high temperature. PA1 (1) Using MCMB whose average grain size is not larger than 10 .mu.m; PA1 (2) Grinding MCMB whose average grain size is not smaller than 10 .mu.m into MCMB whose average grain size is made not larger than 10 .mu.m, then using it; and PA1 (3) Promoting the growth of MCMB, grinding bulkmeso phase grains into MCMB whose average grain size is not larger than 10 .mu.m, then using it.